The present invention concerns a furniture drive for driving a movable furniture part comprising an electric motor, an actuator reciprocatable between two end positions to apply force to the furniture part to be driven, and a transmission connected between the electric motor and the actuator. The transmission has at least one transmission stage in the form of an eccentric transmission with two mutually meshing gears.
For various reasons (lower procurement costs, amount of space required, power requirement), it is desirable to use an electric motor which is as small as possible and which in addition is intended to advantageously manage without a complicated electronic regulating system for torque regulation.
Austrian patent application No A 1542/2007 of earlier priority to the present applicant discloses a furniture drive having a varying transmission ratio which is achieved by an elbow lever arrangement.
EP 1 194 708 B1 describes a drive apparatus for driving an actuator with a transmission stage in the form of an eccentric transmission, the eccentric transmission having two mutually meshing gears. That specification teaches that in many situations of use for transmissions, a maximum drive output torque is required only in one position, in which respect such requirements are said to occur for example in relation to transmissions which perform a closing function.
In accordance with that specification, a drive by way of an electric motor and a transmission with a constant transmission ratio suffers from the disadvantage that the level of the transmission ratio on the one hand must be so high that the maximum torque can be achieved with the electric motor used, which generally requires a high transmission ratio. On the other hand, a high transmission ratio is said to also signify a long setting time for the transmission.
Instead of a transmission with a constant transmission ratio, EP 1 194 708 B1 proposes a two-stage transmission, the first transmission stage being in the form of a shaft transmission (harmonic drive transmission) and the second stage being in the form of an eccentric transmission.
This specification does not teach specific examples of advantageous transmission ratio configurations. Particular attention is directed to the interplay between torque and setting time.
EP 1 194 708 B1 is of only very limited significance by virtue of its fixation with the ratio between torque and setting time in situations of use where that ratio plays only a very subordinate part.
EP 1 898 036 A1 discloses an operating actuator for a vehicle flap provided with an eccentric transmission having two mutually meshing gears. That specification teaches that, in relation to motor vehicle flaps, it is necessary to act on the motor vehicle flap with a sufficiently high torque to overcome the reaction forces caused by a seal during the closing process. That is resolved in such a way that the vehicle flap is actuated by way of a comparatively low transmission ratio during the predominant part of the closing movement. When the motor vehicle flap is approaching the closed position and in particular when it is pressed against a seal, it is driven at a higher transmission ratio.
The opening movement is not discussed in EP 1 898 036 A1, which is to be attributed to the fact that vehicle flaps are mostly opened manually.
Therefore EP 1 898 036 A1 is not relevant in relation to a furniture drive of the general kind set forth, having an actuator which is reciprocated between two end positions.
DE 197 39 851 A1 represents an even more remote state of the art. That specification teaches a windscreen wiper apparatus with two windscreen wiper levers which are driven by a single electric motor, wherein there is provided an eccentric transmission for producing a retardation or an acceleration of the reciprocating movement of the windscreen wiper levers in predetermined regions.